1. Field of the Invention
This invention relates to a heating device for a welding jig having two guide arms with clamping devices for securing the plastic pipe sections or plastic moldings to be welded together. The clamping devices are displaceable in relation to each other. Two semi-circular electrical heating plates are connected or can be connected with each other at their free ends such that their interior receptacles face each other.
2. Description of Prior Art
Such welding jigs are preferably used when welding plastic pipes in a trench. In this application, there is little space for the plastic pipe sections to be connected to each other. The welding process is further impeded where the plastic pipe sections are to be placed as protective pipes on an already existing inner pipe and must be welded together.
A heating device with two pivotably connected heating plates inserted vertically in relation to the plane defined by the two guide arms is known. When pivoted apart, the heating plates can be slipped on the inner pipe. However, the two guide arms limit the opening angle of the heating device. Therefore, an inner pipe with a small diameter requires a welding jig with guide arms sufficiently far apart. However, such a welding jig requires a wide trench.
It is an object of the invention to provide a heating device of the previously mentioned type in which it is also possible to heat outer pipes placed on an inner pipe without using a welding jig in which the guide arms are far apart.
In accordance with this invention, this object is attained due to the radius of the interior receptacles of the heating plates being the same as or greater than the radius of the outer dimension of an inner pipe on which the outer pipe to be welded is slipped and the radius of the outer circumference of the heating plates being greater than the radius of the outer circumference of the outer pipes. In addition, the heating plates have radially outwardly directed extensions at their free ends which have recesses to receive the guide arms of the welding jig. The connecting points of the heating plates are located in the areas of the extensions outside of these recesses for the guide arms.
When the heating plates are opened, the heating device can be slipped on parallel to the plane of connection of the guide arms without the guide arms limiting the opening range of the heating plates. Consequently, the inner pipe can have a diameter which may be considerably larger in relation to the distance between the guide arms than in the known welding jig and heating devices. The heating device of this invention, when applied, is additionally supported and centered by the guide arms, considerably reducing set-up time. Removal of the heating device is also easier.
In embodiments of this invention where one half of each recess is distributed on each free end of the two heating plates, the heating device can be constructed of two almost identical heating plates. In these embodiments of the invention, the distance between the centers of the centering of the plastic pipe sections or plastic moldings held in the clamping devices is also easier. To obtain exact centering, the distance between the centers of the recesses corresponds to the distance between the center longitudinal axes of the two guide arms and the recesses and the center of the closed heating plates is one half of the distance between the centers of the recesses.
In one embodiment of this invention, the heating plates are connected as a non-detachable unit, hinged together at a first set of corresponding extensions, the hinge axis being oriented vertically to the heating surfaces of the heating plates. In another embodiment, the heating plates are adjustably connected to each other at the first set of corresponding extensions, the direction of adjustment extending vertically to the plane of separation of the heating plates.
Securing the heating plates in the closed position is achieved in a simple manner. The second set of corresponding extensions of the heating plates are connected to each other by means of a quick-release closure, for example, a toggle catch.
A compensating movement of the heating plates, necessary during heating, is made possible by the recesses of the first set of corresponding extensions being in the shape of semicircular or rectangular grooves which are one-half of the dimensions of the diameters of the guide arms, and by the recesses of the second set of corresponding extensions being open towards the end of the extensions and in their depth are one-half of the diameters of the guide arms.
The heating device is maintained on one of the guide arms but is displaceable in respect to the other guide arm.